The electronic and semiconductor device industry has a market driven need to increase operational speed and clock rates. As the operational speeds have increased in recent device designs, the maximum operating frequency has become more limited by thermal constraints than by the processing technology's ability to manufacture improved and smaller devices, or the design capability to place and route more transistors and conductors on a given area of semiconductor substrate. For example, it is known that placing too many transistors in a given area may result in what is known as the junction temperature of the device exceeding reliability levels. This is significant because the rate at which the various failure mechanisms in mechanical, electronic and semiconductor devices occur typically obey an exponential law, which may be called the Arrhenius reaction law, and thus an increase in junction temperature of only 10 degrees may result in a doubling of a particular failure rate mechanism.
It is known to prevent a system from overheating by reducing the operating speed if the measured temperature of the system reaches a selected trigger value. Such a method may be known as adaptive throttling. Adaptive throttling methods do not rely upon a knowledge of the past power consumption of the system or use a thermal model of the system. They are reactive methods that respond to the thermal limit being reached, and provide a mechanism for handling variations from the normal operating situation, such as the case of an unexpected high power consumption occurrence. These methods react dynamically to the value of the thermal limitation and reduce the normal operating frequency (for example, a clock rate) to a default lower rate if, for example, the semiconductor junction temperature exceeds a preselected maximum value. Adaptive throttling methods are part of a more general class of control systems that may be known as dynamic thermal management (DTM) methods, which may be reactive like the adaptive throttling, or predictive, and which may use various thermal models to help the predictions. DTM systems may reduce the operating voltage supply value to slow an on-die clock generator to a lower level and thus reduce the thermal output and junction temperature, or DTM systems may adjust both the operating voltage and the clock rate.
An example of a DTM thermal management system might work by dropping the operating frequency or clock rate to half the normal value until the monitored junction temperature drops below the maximum allowable level, and then resetting the operating frequency to the normal value. Another example might be adjusting the operating voltage to a lower value, or adjusting both frequency and operating voltage in response to approaching or passing a thermal constraint value. This is what may be known as a reactive system, and may result in an electronic system repeatedly approaching and surpassing the maximum junction temperature, or some other thermal limit, and then suffer a large drop in system performance until the junction temperature drops below the limit. Other types of control systems may calculate the future effects of current trends in temperature and gradually lower the operating rate to slow or prevent the system from reaching the thermal limitation. Such a system is described in co-pending application Ser. No. 10/934,295 filed Sep. 3, 2004.
Thus there exists a need in the art for an online optimizing controller that may use any type of thermal model to calculate a solution to the full power limit situation, and adjust the calculated solution to account for situations where the input power is not dependent upon assumptions of the upcoming power usage or duty cycle levels. The controller must be able to control the operating rate of the overall system by controlling the thermal limits on some, or all of the subsystems of the electronic system, where each of the controlled subsystems has its own thermal constraints and an operating factor or an operating rate that can affect the thermal performance of the subsystem. The system must account for controlling each element or subsystem to maximize performance without exceeding the elements thermal limit, and the even distribution of power density throughout the entire system.